Growth retardation and delayed pubertal maturation are commonly seen in children with sickle cell disease. Recent evidence suggests that African children with sickle cell disease are under-nourished, have hypoaminoacidemia and a significant loss of essential amino acids in the urine compared with healthy controls. We propose to evaluate the role of urinary excretion of amino acids and hypoaminoacidemia in the growth retardation and poor nutritional status of American children with sickle cell disease.